Screw and nut devices with low internal friction, e.g. so-called ball nut mechanisms, wherein a row of balls are arranged in the thread grooves between nut and screw, have the property of not being irreversible, which in certain cases may be an inconvenience, e.g. in a lifting device, where the load is lifted by such a screw and nut device, this property may cause the load to lower itself when no external driving torque acts upon the device. This may be a safety risk and different braking members, which prevent unintentional movement are earlier known. A helical spring may e.g. enclose the screw and be clamped against it for braking purpose, when the device is loaded in a direction opposite to the driving direction and no driving torque is applied (SE-A-8505997-0). In this known device, the braking spring is located in the thread groove of the screw and it exerts a friction force in these during braking. This implies certain drawbacks. Then wear will occur in the thread, which will reduce the service life of the screw. The friction force, furthermore, will occur at the smallest distance from the rotation axis, when the contact takes place in the bottom of the thread, which gives the smallest possible braking moment for a given frictional force.